This invention relates to a process for the production of partially crystalline polybutene-1 especially suitable for the production of transparent films and sheets.
It is known that films of a highly isotactic polybutene-1 have the disadvantages of low transparency, very different strength values in the longitudinal and transverse directions and therefore a poor tear propagation resistance, which render them unsuitable for many fields of application.
The transparency of the polybutene-1 film can be improved only to a minor extent by increasing the atactic proportion. For example, if the atactic proportion is not separated during processing, together with the polymerization solvent, but instead left in the polymerization product by precipitation with alcohol or by evaporation of the solvent, a polybutene-1 is obtained which has only a small improvement in transparency, even in case of ether-soluble proportions of 10-20%. The tear propagation resistance is not improved as compared to the highly isotactic polybutene-1, which property is very different in the longitudinal and transverse directions, for example, 24.8 kp./mm. longitudinally and 0.89 kp./mm transversely.
In U.S. application Ser. No. 400,899, filed Sept. 26, 1973 and German Patent Application No. P 22 47 786.7, the disclosures of which are incorporated by reference, it has been proposed to produce a polybutene-1 useful for film production by means of a controlled polymerization procedure. The process, which is not described in the published prior art, is characterized in that butene-1 is polymerized with diethyl aluminum monochloride, optionally with the addition of 0.1-1.5% by weight, based on the butene-1, of a comonomer in solution in a high-percentage butene-1 and/or in a C.sub.4 fraction consisting of butene-1, butene-2 and butane, at temperatures of 60.degree.-120.degree. C., with a mixed catalyst of TiCl.sub.3 . nAlCl.sub.3 (n = 0.2 to 0.6), obtained by the reduction of titanium tetrachloride with organoaluminum compounds at temperatures of -10.degree. C. to +30.degree. C. and optionally subsequent tempering at temperatures of 70-150.degree. C.